Device for the creation of containment barriers for cold air in atmospheric conditions corresponding to radiation frosts

ABSTRACT

A mechanical device used to substitute the natural or light material curtains, which are applied so far to prevent the cold air from entering the cultivated areas (situated in very low slope lands) protected from the effects of the radiation frosts by means of the selective drainage of cold air. The referred device put in motion a cold air flow, taken from the ground proximities during frost nights, and impels it producing a jet with an approximately horizontal axe and a circular sector geometry viewed from top.

TECHNICAL AREA

The subject of this application belongs to the technical area of the applied fluid mechanics. It constitutes a device that substitutes the natural and artificial curtains aiming to contain the cold air flux from the exterior to the interior of cultivated areas located on lands with very low slopes, protected from the radiation frost by means of selective drainage of cold air.

BACKGROUND INFORMATION

The use of the selective cold air drainage as a method of frost protection to the crops, has been increasing in the world since the 90's owing to the growing application of the Selective Inverted Sink (SIS). This device is protected by the following patents, of applicant's authorship.

The SIS patents have been registered with the following numbers in the named countries. Country Patent Number Argentina  250341 Chile    652-92 Spain 09201324-4 USA  5647165 Italy  1255171 Uruguay   13387

The SIS can be applied in very different ways to reduce the damage produced by the radiation frost to diverse crops. The application diversity of the SIS is subject, mainly, to the topography of the orchard or vineyard to protect. A case very frequently seen is the one where the orchards to protect are located on large valleys with a practically flat topography (slopes of approx. 1/1000).

In the above mentioned valleys, during frost nights (clear and calm nights with low relative humidity), an increasing cold air accumulation process is generated, producing damages to the crops. A stable atmosphere (stratification with densities decreasing with the height and temperatures increasing with the height) is a characteristic of a cold air accumulation area.

These characteristics are shown in FIG. 1.

To protect these orchards with the SIS, it is necessary to surround the area to be protected with artificial barriers (or curtains) with many metres in height. In that way the SIS drain the cold air in the protected area and the artificial barriers (located on the perimeter of the mentioned area) prevent the coldest layers (the densest ones) from entering the area up to a height above the ground no higher than the artificial barrier. FIG. 2 shows the temperature distribution in the interior and exterior of the area protected by the SIS when they drain the coldest layers in the interior of the mentioned area.

A practical important problem in the application of the SIS commonly is the construction of the mentioned curtains whose needed height can be of various metres. In the common practice the heights required are between 1.5 m and 8.00 m, depending on different factors that are analysed in a case by case basis.

A common way to construct the mentioned curtains is to use fast grow vegetation with a foliage thick enough to prevent the flux of cold air through them. The main problem of this alternative is the long time (many years) needed to reach desired heights, so it is a long term solution to a problem that needs to be solved in most cases within few weeks or months.

Another way to solve the curtain issue is to construct them with light, low cost plastic materials, supported by a steel tube structure, kept in a vertical position by means of turnbuckles secured to the ground. The advantage of this constructive method is that it is possible to set the entire curtain in few days. The main problems of this kind of curtain are: they are vulnerable to strong winds, visual obstruction of the natural environment, the need to obtain special permissions to set the curtain, and the obstruction the curtain may cause to the free circulation of vehicles in the orchard. Besides, these light curtains demand maintenance during the frost risk season and a continuous supervision during frost nights.

It also must be said that, occasionally, the sole use of natural or artificial curtains, with no need to use the SIS, constitute a very effective way of protection against the damage produced by radiation frost. That is because the natural or artificial curtains, strategically located in the orchard, divert the cold air currents that otherwise would invade the orchard to protect.

As it has been exposed before, in the range of solutions to control the radiation frost, based on the modification of the cold air circulation over the orchard, it is of great practical interest the construction of barriers which are free from the problems detailed above associated with the light materials used in the construction of the natural and artificial curtains.

SUBJECT OF THIS APPLICATION

The subject of the current patent application is a device that fulfils the function of containing the cold air flux, the same way a material barrier does, but using moving cold air as a holding factor. The above mentioned device captures the coldest air which is near to the ground and expels it, in the form of a jet, directed towards the cold air mass to be contained. This jet has an approximate horizontal axe and its dynamic characteristics (geometry and velocity field) are adequate to the fulfilment of the holding function required. Such dynamic characteristics are determined by the geometry of the device outlet duct and by the discharge the device put in motion. The kinetic energy acquired by the cold air since it is captured by the device until it is expelled in the jet, is proportioned by a fan located in the interior of the device.

The referred device performs three functions. The first one is the air flow intake which is put in motion. Such intake must be carried out minimizing the localized loss of head, and also within a small distance from the soil in order to maximize the average density of the captured air. The second is the drive of the above mentioned flow transferring mechanical power to the fluid. The third one is the discharge of air to the atmosphere minimizing the localized loss of head and allowing the conformation of a jet with an approximately horizontal axe, as it was already mentioned before, whose dynamic structure will be the most adequate to fulfil the function of preventing the coldest layers, which surround the perimeter of the area, from entering the protected area.

DEVICE DESCRIPTION

In FIGS. 3, 4 and 5 can be appreciated sketches of the device in elevation, top view and section.

The intake of the air flow in motion is made through a hollow cylindrical structure, circular or regular polygon in section, with a vertical axe (1) (see FIG. 5) The air circulation occurs from bottom to top. The cylindrical structure (1), in its straight inferior section (closest to the ground), locks on a conical structure (2) (bell shaped or trumpet-shaped), whose axe coincides with the axe of the already mentioned cylindrical structure (1) The section of the above mentioned conical structure (2) increases downward (larger section when approaching the ground) The conical structure (2) ends (in the end closest to the ground) in a planar straight section and open (3), perpendicular to the cone axe through which the air enters to the device. The section (3) is from the ground a distance which can vary according to the flow moved by the device. Such variation can be achieved adjusting the level of the legs (4) which support the device on the ground.

The flow drive is produced by means of a standard fan (5) whose characteristics with regard to its kind, diameter, discharge and static head will be the adequate to the desired jet shape.

The drive occurs using an outlet structure (6) which takes the flow at the exit of the fan and introduces it in various flux tubes (7) which conduct the mentioned flow to a discharge section (8) which in turn distribute it uniformly in accordance with a circular sector (seen from the top) with an angle to the centre not less than 60° and not greater than 180°. The velocity at the discharge section (8) will be approximately horizontal and with an average magnitude sufficiently enough so as to prevent the coldest layers (which surround the perimeter of the area) from entering the interior of the protected area.

Having previously determined the nature of the invention and having described it, showing the way it can be put into practice, the embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows: 

1. A mechanical device used to substitute the natural or light material curtains, which are applied so far to prevent the cold air from entering the cultivated areas protected from the effects of the radiation frosts by means of the selective drainage of cold air. The referred device put in motion a cold air flow, taken from the ground proximities during frost nights, and impels it producing a jet with an approximately horizontal axe and a circular sector geometry viewed from top.
 2. A device according to claim 1 characterized by: a. a cylindrical structure, circular or regular polygon in section, with a vertical axe which locks on its lower end (nearest to the ground) with a conical part (bell shaped or trumpet-shaped) whose axe coincide with the cylindrical structure previously described. In the mentioned conical part, the section increases downwards. The cone ends in a right open and planar section, perpendicular to the cone's axe, with a distance to the ground that can vary according to the flow mobilized by the device. This variation can be achieved adjusting the legs which support the device on the ground. b. a standard fan whose characteristics regarding its kind, diameter, discharge and static head will be the adequate to the desired jet shape. c. a structure which takes the flow at the exit of the fan and introduces it in various flux tubes which conduct the mentioned flow to a discharge section, which in turn distribute it uniformly in accordance with a circular sector (seen from the top) with an angle to the centre not less than 60° and not greater than 180°. The velocity at the discharge section will be approximately horizontal and with an average magnitude sufficiently enough so as to prevent the coldest layers (which surround the perimeter of the area) from entering the interior of the protected area. 